1. Field of the Invention
The present invention relates to an air bag of an air bag apparatus to be carried on board a vehicle and, in particular, to a plane-type air bag, which can be formed by joining together the respective outer peripheral edges of a pair of bag cloths substantially identical in the outer shape with each other.
2. Description of the Related Art
Conventionally, as disclosed in JP-9-263204, there is known a plane-type air bag that can be formed by joining together the respective outer peripheral edges of a pair of bag cloths substantially identical in the outer shape with each other.
The air bag disclosed in the cited publication includes a pair of circular-shaped wall portions substantially identical in shape with each other; specifically, one is a vehicle body side (steering wheel side) surface, and the other is an occupant side (driver side) surface. And, the air bag is formed by sewing and joining together the respective outer peripheral edges of the vehicle body side and occupant side surfaces. Also, in the interior of the air bag, there is disposed a tether which is used to restrict the mutual spacing distance between the vehicle body side and occupant side surfaces when the air bag is deployed. The tether is disposed so as to join the peripheral edge of an opening for inflator insertion to the portion of the occupant side surface that is opposed to the opening.
However, in the above plane-type air bag, since the respective outer peripheral edges of the vehicle body side and occupant side surfaces are joined, there is found the following problem. That is, it is difficult to increase the thickness of the peripheral edge of the air bag in the deployment thereof to thereby dispose a portion having an increased capacity, for example, between the abdomen of the occupant (driver) and the ring portion of a steering wheel.
To increase the thickness of the outer peripheral edge of the air bag, the air bag cloths may be sewn together into a three-dimensional shape to form an air bag. However, in the case of such a three-dimensional air bag, it is impossible to employ an easy producing step, as in the case of a plane-type air bag, in which the air bag cloths can be developed flat, the occupant side and vehicle body side surfaces can be superimposed on top of each other, and the occupant side and vehicle body side surfaces can be sewn and joined together. That is, it takes much time and labor to manufacture the three-dimensional-shaped air bag.